There is a damper device called, i.e. a rotary damper and the like, comprising a rotor (rotation-side member); a stator (fixed-side member, a housing in a prior art document); and a viscous fluid filled therebetween, and formed such that a resistance of the viscous fluid relative to a rotation or a relative rotation of the rotor becomes a braking force (see Patent Document 1).
In the damper device of the Patent Document 1, the housing has a structure wherein the rotor can be housed in an annular space formed between an outer cylinder and an inner cylinder. In the damper device of the Patent Document 1, the rotor has a cylinder shape wherein both cylinder ends are open, and the inner cylinder of the housing opens both cylinder ends as well. Consequently, the damper device of the Patent Document 1 prevents leakage of the viscous fluid between the rotor and stator by two seal members of an annular first seal member mounted outside the rotor, and an annular second seal member mounted inside the rotor.
Therefore, in the damper device of the Patent Document 1, when the rotor and the stator are assembled, the first seal member is fitted to an outside of the rotor in such a way as to pass the rotor through the inside while elastically expanding the first seal member, and from a state wherein the second seal member is housed inside the rotor, it is necessary to house the rotor inside the annular space of the stator. In such an assembly, it is required to pay special attention to a positional misalignment, a dropout, or the like of any of the seal members. In the assembly, in a case wherein a position of any of the seal members is misaligned, or a twist or the like is generated in any of the seal members, there occur inconveniences such that a sealing property of the viscous fluid becomes insufficient, and the damper device does not exert an expected braking force, and the like.